Insulin and other injectable medications are commonly given with syringes into the intradermal layer of the skin and other dense tissues. Intradermal medication injections result in faster uptake of the medication, thereby resulting in improved therapy. Such injections require higher injection pressures, upwards of 200 psi, than traditional subcutaneous injections.
Techniques and devices are known for administering an injection into the intradermal region of the skin. One method, commonly referred to as the Mantoux technique, uses a “standard” needle and syringe, i.e., a syringe typically used to administer intramuscular or subcutaneous injections. The health care provider administering the injection follows a specific procedure that requires a somewhat precise orientation of the syringe with regard to the patient's skin as the injection is administered. The health care provider must also attempt to precisely control the penetration depth of the needle into the patient's skin to ensure that it does not penetrate beyond the intradermal region. Such a technique is complicated, difficult to administer, and often may only be administered by an experienced health care professional.
A conventional syringe 101 is shown in FIG. 1. The needle 103 is sufficiently long to deliver the drug to the subcutaneous region of the skin. However, a user would not be able to easily deliver the drug to the intradermal region of the skin, as discussed above.
Existing drug delivery pens offer several advantages over syringe-based systems for delivering insulin subcutaneously. Reusable drug delivery pens hold 20 or more doses without requiring the drug cartridge to be refilled. Dose setting is achieved simply with the use of a dial. However, those injection systems are designed for low pressure subcutaneous injections. Intradermal injection of insulin and other medications provides faster uptake of the drug, thereby leading to improved therapy. Existing drug delivery pens have several limitations regarding intradermal drug delivery. First, the mechanical advantage provided by the pen is minimal and requires the user to supply upwards of 20 lbs of force to generate sufficient pressure. Second, the pen components can be damaged by this high force, resulting in leaking and inaccuracy at the high pressures.
Drug delivery pens, such as the exemplary drug delivery pen 100 shown in FIGS. 2 and 3, are designed for intradermal injections and typically comprise a dose knob/button 24, an outer sleeve 13, and a cap 21. The dose knob/button 24 allows a user to set the dosage of medication to be injected. The outer sleeve 13 is gripped by the user when injecting medication. The cap 21 is used by the user to securely hold the drug delivery pen 100 in a shirt pocket, purse or other suitable location and provide cover/protection from accidental needle injury.
FIG. 3 is an exploded view of the drug delivery pen 100 of FIG. 2. The dose knob/button 24 has a dual purpose and is used both to set the dosage of the medication to be injected and to inject the dosed medicament via the leadscrew 7 and stopper 15 through the medicament cartridge 12, which is attached to the drug delivery pen through a lower housing 17. In standard drug delivery pens, the dosing and delivery mechanisms are all found within the outer sleeve 13 and are not described in greater detail here as they are understood by those knowledgeable of the prior art. The distal movement of the plunger or stopper 15 within the medicament cartridge 12 causes medication to be forced into the needle 11 of the hub 20. The medicament cartridge 12 is sealed by septum 16, which is punctured by a septum penetrating needle cannula 18 located within the hub 20. The hub 20 is preferably screwed onto the lower housing 17, although other attachment means can be used, such as attaching to the cartridge. To protect a user, or anyone who handles the pen injection device 100, an outer cover 69, which attaches to the hub 20, covers the hub. An inner shield 59 covers the patient needle 11 within the outer cover 69. The inner shield 59 can be secured to the hub 20 to cover the patient needle by any suitable means, such as an interference fit or a snap fit. The outer cover 69 and the inner shield 59 are removed prior to use. The cap 21 fits snugly against outer sleeve 13 to allow a user to securely carry the drug delivery pen 100.
The medicament cartridge 12 is typically a glass tube sealed at one end with the septum 16 and sealed at the other end with the stopper 15. The septum 16 is pierceable by a septum penetrating cannula 18 in the hub 20, but does not move with respect to the medicament cartridge 12. The stopper 15 is axially displaceable within the medicament cartridge 12 while maintaining a fluid tight seal.
The backpressure in subcutaneous injections is not very large, while the backpressure associated with intradermal injections may be many times greater than that of subcutaneous injections. Existing drug delivery pens require a large force to inject medication into the intradermal layer, thereby making the intradermal medication injection difficult. For example, the backpressure often exceeds 200 psi for an intradermal injection, while the backpressure for a subcutaneous injection is generally in the range of 30-50 psi. Thus, a need exists for a drug delivery pen that provides a mechanical advantage to facilitate an injecting a medicament dose intradermally. Furthermore, the drug delivery pen components can be damaged due to the high pressures associated with intradermal injections, thereby resulting in medication leakage and dose inaccuracy.